OBJECTIVES: 1. To define the mechanism and significance of the reaction of tissue thromboplastin (Tissue factor) with the complement system, and 2. To investigate the participation of complement in platelet aggregation and sudden death induced by the administration of arachidonic acid. METHODS: 1. Quantitation of complement components in serum treated with thromboplastin. 2. Purification of thromboplastin and complement components by salt fractionation, chromatography and electrophoresis; determination of biological activity. 3. Characterization of thromboplastin-complement component complexes by gel filtration chromatography and ultracentrifugation. 4. Platelet counts and complement determination in normal and C6 deficient rabbits injected with arachidonic acid. 5. In vitro studies of platelet aggregation and release induced by arachidonic acid with platelets from normal and C6 deficient rabbits; measurement of complement components and prostaglandins in plasma after aggregation and removal of the platelets.